INTERNAL OXIDATION OF VACANCY AGGLOMERATES IN CZOCHRALSKI SILICON-WAFERS DURING HIGH-TEMPERATURE ANNEALS

Fast pulled Czochralski silicon crystals usually contain large octahed ral vacancy agglomerates. These voids are known as D defects, which de grade the integrity of thin gate oxides by causing time zero dielectri c breakdown. After annealing the wafers at temperatures above 1100 deg rees C, the gate oxide integrity is clearly improved. We show by theor etical estimation, light-scattering tomography and transmission electr on microscopy studies that the vacancy agglomerates can be filled with silicon oxide by internal oxidation. This is brought about by diffusi on of interstitial oxygen to the voids, which can be regarded as inter nal surfaces. In this way they become less detrimental for thin gate o xides, because now they consist of silicon oxide itself. However, they are still present in an octahedral-like geometry and can be observed by Brewster angle infrared light-scattering tomography. (C) 1998 Ameri can Institute of Physics.